INSULIN-RECEPTOR SUBSTRATE-1 IS EXPRESSED AT HIGH-LEVELS IN ALL CELLSOF THE PERIIMPLANTATION MOUSE EMBRYO

Insulin and insulinlike growth factors are important for embryonic gro wth and metabolism. Intracellular transduction far these factors has n ot been studied in the preimplantation mouse embryo. Peri-implantation mouse embryos synthesize insulinlike growth factor (IGF)-II ligand, i nsulin receptor, IGF-I receptor, and IGF-II receptor and respond to IG F-II, IGF-I, and insulin metabolically and mitogenically. Maternal tis sues in the oviduct and uterus are also sources of IGF-I and insulin. Signaling of IGFs occurs through insulin receptor substrate (IRS)-1 an d IRS-2. This paper shows that IRS-1 mRNA and protein are highly expre ssed in preimplantation mouse embryos, in embryonic cell lines, and in cultured blastocyst outgrowths. IRS-1 mRNA and protein are detected i n embryo-derived cell lines cultured to produce the three cell lineage s (stem cells, endoderm, and trophoblast cells). IRS-1 mRNA is detecte d by reverse transcription-polymerase chain reaction (RT-PCR) in the E 3.5 blastocyst before implantation and in F9 teratocarcinoma stem cell s and parietal endoderm cells. IRS-1 mRNA is detected by Northern blot hybridization at high levels in stem cells and in differentiated prog eny of F9 cells and C3H/NE trophectoderm cells. IRS-1 protein was dete cted in these cell lines and in an overexpressing CHO-IRS-1 fibroblast cell line by immunocytochemistry. Cultured blastocyst outgrowths are a model for implantation events of the trophoblast/placenta lineage an d endoderm/yolk sac lineage. In the blastocyst outgrowth, IRS-1 protei n is detected in inner cell mass cells (ICM cells), primitive endoderm , parietal endoderm, and trophectoderm cells. These data suggest that IRS-1 is expressed in art cell lineages of the peri-implantation mouse embryo and mediates some effects of insulin and IGFs at this stage. ( C) 1998 Wiley-Liss, Inc.